The correct answer is option 2, Red. Endangered species are listed in the Red Data Book. The Red Data Book is a comprehensive record of threatened and endangered species of animals, plants, and fungi. It is used by conservation organizations and governments to identify and monitor species at risk of extinction. The Red Data Book provides information on the conservation status, distribution, and threats to each listed species. The red color is used to signify the urgency and critical status of these species, indicating the need for immediate conservation action to prevent their extinction. So, when looking for information about endangered species, it is important to refer to the Red Data Book.